#!/usr/bin/env ruby
# echo.rb - display a line of text
VERSION = "0.2"

# help and version
if ARGV.size == 1
  if ARGV[0] == "--help"
    puts <<-'END'
Usage: /usr/bin/echo [SHORT-OPTION]... [STRING]...
  or:  /usr/bin/echo LONG-OPTION
Echo the STRING(s) to standard output.

  -n             do not output the trailing newline
  -e             enable interpretation of backslash escapes
  -E             disable interpretation of backslash escapes (default)
      --help     display this help and exit
      --version  output version information and exit

If -e is in effect, the following sequences are recognized:

  \\      backslash
  \a      alert (BEL)
  \b      backspace
  \c      produce no further output
  \e      escape
  \f      form feed
  \n      new line
  \r      carriage return
  \t      horizontal tab
  \v      vertical tab
  \0NNN   byte with octal value NNN (1 to 3 digits)
  \xHH    byte with hexadecimal value HH (1 to 2 digits)

NOTE: your shell may have its own version of echo, which usually supersedes
the version described here.  Please refer to your shell's documentation
for details about the options it supports.
    END
    exit
  end

  if ARGV[0] == "--version"
    puts File.split(__FILE__).last + " " + VERSION
    exit
  end
end

def isxdigit?(c)
  case c
  when '0'..'9', 'A'..'F', 'a'..'f'
    return true
  else
    return false
  end
end

def isoctal?(c)
  case c
  when '0'..'7'
    return true
  else
    return false
  end
end

# Convert C from hexadecimal character to integer.
def hextobin(c)
  case c
  when 'a', 'A'
    return 10
  when 'b', 'B'
    return 11
  when 'c', 'C'
    return 12
  when 'd', 'D'
    return 13
  when 'e', 'E'
    return 14
  when 'f', 'F'
    return 15
  else
    return c.to_i
  end
end

def just_echo
  # join tmpargv array (with valid options removed) into a string
  argv = $tmpargv.join(" ")

  if $do_v9
    i = 0
    while i < argv.size do
      c = argv[i]
      if c == "\\"
        i += 1 # next char
        case argv[i]
        when 'a'
          c = "\a"
        when 'b'
          c = "\b"
        when 'c'
          exit
        when 'e'
          c = "\x1B"
        when 'f'
          c = "\f"
        when 'n'
          c = "\n"
        when 'r'
          c = "\r"
        when 't'
          c = "\t"
        when 'v'
          c = "\v"

        # handle HEX
        when 'x'
          # FIRST DIGIT
          i += 1 # next char
          ch = argv[i]
          if ! isxdigit?(ch)
            print "\\x"
            next
          end

          # 2ND DIGIT
          i += 1 # next char
          c = hextobin(ch)
          ch = argv[i]
          if isxdigit?(ch)
            c = c * 16 + hextobin(ch)
            c = c.chr
          else # 2nd hex digit invalid, print both
            print c.chr
            print ch
            i += 1 # next char
            next
          end

        # handle octal
        when '0', '1', '2', '3', '4', '5', '6', '7'
          if argv[i] == '0'
            i += 1 # next char
          end

          c = 0

          # 1st or 2nd digit
          if isoctal?(argv[i])
            c = c * 8 + argv[i].to_i
          else
            print c.chr
            next
          end

          # 2nd or 3rd digit
          i += 1 # next char
          if isoctal?(argv[i])
            c = c * 8 + argv[i].to_i
          else
            print c.chr
            next
          end

          # 3rd or 4th digit
          i += 1 # next char
          if isoctal?(argv[i])
            c = c * 8 + argv[i].to_i
          else
            print c.chr
            next
          end

          # convert decimal value to character
          c = c.chr

        #when '\\'
        end
      end
      print c
      i += 1 # next char
    end

  else # don't handle backslash escapes (default)
    print argv
  end

  puts if $display_return # newline (default)
  exit
end

# copy ARGV because we may remove some elements from it
# and then our loop will be fucked
$tmpargv = ARGV.dup # make sure to use DUP!

# Global options
$do_v9, $display_return = false, true

# Parse arguments
ARGV.each do |arg|
  if arg[0] == '-'
    temp = arg[1..-1] # remove '-'

    # validate all options after '-'
    temp.each_char do |c|
      case c
      when 'e', 'E', 'n'
        # next
      else
        # Any char besides 'e', 'E', 'n' and the whole string is echoed
        just_echo
      end
    end

    # If we get here, all options in temp are valid
    temp.each_char do |c|
      case c
      when 'e'
        $do_v9 = true
      when 'E'
        $do_v9 = false
      when 'n'
        $display_return = false
      end
    end

    # REMOVE VALID arg from tmpargv
    # ARGV controls loop iteration so we can't delete from it
    $tmpargv.slice!($tmpargv.index(arg))

  else
    just_echo # if the string doesn't begin with '-' we are done parsing
  end
end